This usually means that there is mixed content coming from an open HTTP connection present on a secure HTTPS page. Firefox doesn't block mixed passive content by default, but shows a padlock with a yellow exclamation mark. You can click this special icon for more information. *https://support.mozilla.org/en-US/kb/mixed-content-blocking-firefox *https://support.mozilla.org/en-US/kb/tracking-protection-firefox *https://support.mozilla.org/en-US/kb/control-center-site-privacy-and-security-firefox The Web Console displays what specific content this is about. *"3-bar" menu button or Tools -> Web Developer *https://developer.mozilla.org/en-US/Tools/Web_Console

Perhaps your next question is, "Should I be concerned?" It depends on the type of site. If it's your bank, or another site that handles sensitive information, RED ALERT. If it's a discussion board, not really a problem.